1. Field of the Invention
The present invention generally relates to apparatuses and methods for authenticating digital signatures and computer-readable recording media having a program recorded therein for causing a computer to authenticate a digital signature, and more particularly to an apparatus and a method for authenticating a digital signature, and a computer-readable recording medium having a program recorded therein for causing a computer to authenticate a digital signature, in which apparatus, method and medium the digital signature is formed by a random unintelligible number or character string and a signature mark of a signer can be built into image information so that the digital signature can be visually recognized.
2. Description of the Related Art
In a network such as a client/server system shown in FIG. 1, a plurality of clients and a server are connected through the network. In such a network system, an electronic decision system is widely known in which a decision transaction is conducted by utilizing GroupWare.
In the electronic decision system, a digital signature is used. For example, in FIG. 1, a user A of a client A attaches a digital signature to a document created by the user A and then sends the document to a user B of a client B through the network. The user B of the client B obtains a public key for decrypting the digital signature of the user A of the client A and decrypts the digital signature attached to the document received from the user A by using the public key. When the digital signature is successfully decrypted, the document is authenticated so as to be sure that the document was sent from the user A and was not tampered with. As described above, it is possible to authenticate a document author (document sender) by using the digital signature. Thus, it is not required for the document author to print out a created electronic document onto a paper sheet and then stamp a personal seal on this paper sheet where the created electronic document was printed.
However, the conventional digital signature described above has disadvantages.
Generally, the digital signature is formed by a random unintelligible number or character string. Thus, the digital signature can not be recognized easily by human eyes while a stamped seal identifying the document author can be easily recognized by human eyes. Accordingly, it is difficult for a receiver which has received the created electronic document from the document author to distinguish a difference between a legal digital signature and an illegal digital signature of the document author. Also, the digital signature formed by an unintelligible number or character string makes the receiver uncomfortable and it is required for the receiver to decrypt the digital signature.
Moreover, the digital signature recently has become 512 to 1024 bits in length. Compared with the seal stamped on the paper sheet, a larger space is required to show the digital signature.
Also, the digital signature conventionally has another disadvantage in that a position of the digital signature is limited to an end of the created document, while there is no limitation on where to stamp a seal on the paper sheet.